Igneous Origin of some Trap Rocks. 129 



swept away in the progress of time, and that they were subjected to 

 a vast pressure of solid materials, and not improbably of the ocean ; 

 the ancient ocean which enveloped the globe, before it attained its 

 habitable condition. 



If fire were the agent, it is not now necessary to stop to account 

 for it ; for its existence at the present moment, and in all ages, is an 

 unquestionable fact, and must be admitted, whatever theories of its 

 origin we adopt or reject, and no geologist will question the original, 

 or at least early submergence, of our planet under a deep ocean. 



If then we suppose that the materials of the trap rocks were melted 

 below, and were forced upward through the incumbent strata, either 

 from fissures or vents, and that upon those superior strata, the ocean 

 itself was also incumbent, we have all the conditions necessary for 

 the solution of this problem.* Had the trap rocks been erupted into 

 day light like currents of lava, there would be no reason why they 

 should not exhibit all the variety of appearance that belongs to lavas ; 

 but, if only forced through, and among superior strata, or even if 

 forced quite through them, but still remaining under the pressure of 

 many miles of ocean ; they would congeal under enormous pressure, 

 and of course would be long in cooling, and would in the main as- 

 sume the stony or rocky, rather than the vitreous character. Sir 

 James Hall, and Mr. Gregory Watt proved, a good many years since, 

 that trap rocks, if melted and cooled very slowly, and under press- 

 ure, do, in fact, reassume the stony and subcrystalline appearance ; if 

 rapidly and without pressure, they become vitreous, and the same 

 pieces may be made to pass from one stage to the other at pleasure ; 

 the slag becoming rock again, and the rock again slag ;f the same 

 fact is true also, of acknowledged lavas. 



In the case of the Hartford quarry, if we suppose that the melted 

 trap came in contact with the argillaceous sandstone, still charged 

 with abundant moisture, which the evident circumstances of its depo- 

 sition would necessarily imply,f and replete too with carbonic acid in 



*■ All compound rocks are fusible, and as we have every reason to believe are ac- 

 tually melted in volcanos : trap is fusible in our furnaces, and bottles were some 

 years since in France, blown from this material. I have melted the New Haven 

 trap, so that it flowed and congealed on the grates of the furnace in stalactites. 



t I saw the specimens of Sir James Hall, (father of Capt. Basil Hall, the celebrated 

 traveller in America.) They were exhibited by Dr. Hope, at one of his public lec- 

 tures during his discussion of the HuttOnian theory. 



|. If any proof were wanting that this class of locks was laid down under water, it 

 is at hand, 'n quarrying the coarse con!;;!omerate sandstone, (a part of the very 



Vol. XVJL— No. 1. 17 



V 



